The present invention relates to a computer network architecture for switching data between individual input and destination resources. More specifically, the present invention discloses an apparatus and a method of controlling a plurality of switches connected together as a single stacked switching system.
A conventional switching system for interconnecting and switching data between a plurality of input/destination resources, e.g., computer terminals, represents a rapidly developing area of technology. However, as the number of input/destination resources increases, the number of ports supported by a single switch can no longer handle the network traffic needs of a modern system. In addition, with the proliferation of the modern virtual local area network (xe2x80x9cVLANxe2x80x9d) environment, the need for an economic high performance switching system capable of handling increasingly higher numbers of user and/or workgroups is increased.
Ethernet switches first appeared in 1991 when Kalpana((trademark)) launched the original ethernet switch. From an ethernet perspective, however, switches are really just multiport bridges that have been around for many years. Technically, bridging is an OSI Layer 2 function, and all of today""s common networking standardsxe2x80x94such as the three different ethernet standards, token ring, FDDI, and so onxe2x80x94can all be bridged. What differentiate today""s switches from yesterday""s bridges are the features and the uses of these modern multiport bridges.
A few years ago, two-port ethernet bridges were used to connect two different local area networks (xe2x80x9cLANsxe2x80x9d) together. Then vendors started building intelligent multiport bridges, which are essentially a number of two-port bridges connected together. Today, these multiport bridges have been enhanced and are called switches. These switches are now used within an existing network to disconnect or segment a larger LAN into many smaller ones.
On the other hand, a repeater is a network device that indiscriminately regenerates and forwards a received ethernet frame, whether it""s good or bad. Repeaters are known as passive, or shared, components of the network because they do not logically act on incoming frames. Repeaters just regenerate incoming signals, thus extending the diameter of the network. In this way, repeaters are invisible to network events such as collisions or errors, merely propagating them along. Hence, a repeater cannot extend the collision domain of a network. In other words, repeaters simply enlarge an existing network.
Quite differently, bridges connect different ethernet LANs. More specifically, bridges perform basic frame filtering functions before retransmitting the incoming frame. Whereas repeaters forward all frames, a bridge forwards only those frames that are necessary. If a frame does not need to be forwarded, the bridge filters it out.
For example, a bridge can be used to eliminate unnecessary network traffic from an ethernet LAN to another ethernet LAN by screening the traffic. Bridges also do speed matching: Regular 10 Mbps ethernet and 100 Mbps fast ethernet can only be connected by means of a bridge.
Specifically, every ethernet frame has two fields defined as the destination and source address. These two fields tell a bridge where a frame is originated and where it is ultimately destined. Bridges look at an incoming ethernet frame and analyze the destination address defined in the frame""s header. From this information, the bridge can check its internal memory for past frames and determine whether to forward the frame to another port or filter it outxe2x80x94that is, do nothing and discard the frame. In this way, bridges can isolate network traffic between network segments. In some cases, bridges can also check for errors and don""t forward damaged or incomplete frames.
A bridge works like a good postal mail delivery system. A bridge knows exactly where everyone within its served neighborhood resides. It delivers a piece of mail only to the intended recipient within its served neighborhood, looking at the address on every envelope and delivering the envelope to that particular address. If an envelop or frame is damaged or contains an error, a bridge mail system will not, delivery nor forward the mail to the intended recipients. Furthermore, if an envelop or frame indicates an address belonging to a neighborhood served by another bridge, the envelop or frame will be relayed to that bridge accordingly.
A repeater works very differently. A repeater mail system uses the brute-force approach to mail delivery. A repeater makes a copy of every piece of mail it receives, then delivers a copy to you and everyone in your neighborhood. Everyone in the neighborhood gets not only his or her own mail but also copies of everyone else""s mail.
A stackable repeater can be thought of as a repeater with an expansion option. A stackable repeater consists of several independent units, each with a given number of ports. Each unit acts as a standalone repeater in its own right, but also has an external connection for adding additional units exactly like itself. Because stackable repeaters are shared-media devices, the effective bandwidth for a stack of hubs is always the same, no matter how many ports are in the stack. The more ports that are added, the less average bandwidth available to any given port.
The stackable repeater""s upgradability and inexpensive cost per port combine to make it the fastest growing segment of the entire hub market. Stackable repeaters allow LAN administrators to purchase a single management unit to manage the whole stack, and thereby distribute the management costs over many ports. Stackable repeaters are also extremely useful in connecting many nodes on an ethernet network due to the associated network diameter restrictions.
Stackable repeaters are analogous to multiple standalone repeaters linked together with a high-speed stacking bus, yet sharing the same collision domain. This makes the stacked repeater look to the rest of the network like essentially one large repeater. Stackable repeaters are currently quite popular in 10 BASE-T, and newer 10/100 versions.
Stackable repeaters are becoming popular because they offer multiple connections at a low cost per port, they are manageable and easy to upgrade, and they fit well within the typical hierarchical network structure of large LANs.
As network traffic grows, a new switch design is required to accommodate the increasing number of ports connected to a switch. Attempts have been made to combine a plurality of switches to form a stacked switching system. However, because of the complexity in handling the stacked management functions, it has been very difficult to combine multiple switches into a stacked switching system. There are currently some stackable switches available in the market, however, most of these stackable switches require a dedicated system management unit to coordinate various switches in the stacked system. In some conventional designs, this dedicated system management unit is a separate hardware component loaded with stacked management software/firmware. By connecting this system management unit to each of the switch units in the stacked switching system, the system management unit acts as a master control of the stacked system. However, these separate system management units tremendously increase the cost and physical dimension of the stacked switching system. Thus, a new method of combining a plurality of switches together in forming a new stacked switching system as disclosed in the present invention is desired.
It is therefore an object of the present invention to provide a method of connecting a plurality of switching units.
It is another object of the present invention to combine a plurality of switching units to form a stacked switching system.
It is yet another object of the present invention to provide a flexible control to the switches connected as a stacked switching system.
It is a further object of the present invention to provide a number of design topologies for controlling a stacked switching system.
The present invention discloses an apparatus and a method of controlling a stacked switching system. The stacked switching system according to the present invention comprises a plurality of switches connected to each other through a network backplane. One of the switches in the stacked system is designated as the master unit, whereas the remaining switches are designated as the slave units. The present invention discloses two topology designs to assign the master duties among the plurality of switches. The first topology design is termed as a fixed topology and the second topology design is termed as a dynamic topology. Both of these two topology designs assign the master control to the switch having the highest priority index. The assignment of this master control is performed whenever there is a change of topology in the system such as the deletion or addition of switching unit to the system. For the fixed topology design, the master control assignment can only be performed after rebooting the system. On the other hand, for the dynamic topology design, the master control assignment can be performed xe2x80x9con-the-flyxe2x80x9d which means the master control assignment can be performed without the need of rebooting the system.
Additional objects, features and advantages of various aspects of the present invention will become apparent from the following description of its preferred embodiments, which description should be taken in conjunction with the accompanying drawings.